Emerging jets are characteristic for models with a composite dark sector. CMS has studied such a model [1]}, which contains a heavy mediator \(\mathrm {X_{DK}}\)  that couples both to dark sector and SM particles. The experimental signature consists of four high-\(p_\mathrm {T}\)  jets, two from down quarks and two from dark quarks [2]}. The dark quark jets contain many displaced vertices arising from the decays of dark pions (\(\pi _{\mathrm {DK}}\) ) produced in the dark parton shower and fragmentation.The trigger was a simple \(H_\mathrm {T}\)  trigger with a threshold of 900 GeV, and the event selection required two jets with displaced tracks and many different vertices within the jet cone, and two regular jets. The main background is SM four-jet production, where jets are tagged as emerging either because they contain long-lived B mesons or reflect track misreconstruction. It is estimated with a data-driven method and depends on parton flavour and track multiplicity, as can be seen from Fig. REF  (left).
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